1. Field of the Invention
The present invention relates to a portable power working machine, such as a bush cutter, that drives an actuating part, such as a cutting blade, provided at a distal end of an operating arm with an electric motor.
2. Description of the Related Art
Portable power working machines, such as portable bush cutters, are generally used for cutting weeds on footpaths between fields, undergrowth and grass in forests, etc.
As an example of this type of bush cutter, Japanese Unexamined Patent Application Publication No. 2004-8054 discloses a bush cutter including a pipe-shaped operating arm, a drive shaft extending through the operating arm, an engine provided at a proximal end of the operating arm and caused to rotate the drive shaft, and a cutting blade disposed at a distal end of the operating arm and rotated by the rotation of the drive shaft. This bush cutter has a loop strap attached to the operating arm at a position near the proximal end thereof, and an operator carries the bush cutter by placing the strap around the shoulder. In this state, the operator holds a bar-shaped handle provided on the operating arm and moves the operating arm in the front-rear and left-right directions to cut weeds and the like.
In densely housed areas, such as urban areas, where quietness is required, bush cutters having electric motors as a power source are often used instead of bush cutters having engines as a power source. An example of a bush cutter including an electric motor as a power source is described in Japanese Unexamined Patent Application Publication No. 6-62637. This bush cutter includes a pipe-shaped operating arm; a motor housing connected to a distal end of the operating arm; an electric motor contained in the motor housing and having a fan attached thereto; a cutting blade disposed below the motor housing and driven by the electric motor; and a battery housing containing a battery and disposed at a proximal end of the operating arm. An inlet and an outlet for cooling air are formed in the battery housing and the motor housing, respectively.
This bush cutter has a loop strap attached to the operating arm at a position near the proximal end thereof, and an operator carries the bush cutter by placing the strap around the shoulder. In this state, the operator activates the electric motor, and accordingly the cutting blade and the fan starts to rotate. The operator holds a handle provided on the operating arm and moves the operating arm in the front-rear and left-right directions to cut weeds and the like with the rotating cutting blade. At the same time, atmospheric air is drawn into the battery housing through the inlet as cooling air due to the rotation of the fan. The air flows through the operating arm and the motor housing, and is discharged into the atmosphere through the outlet. The cooling air cools the battery and the electric motor.
The bush cutter described in Japanese Unexamined Patent Application Publication No. 6-62637 causes less noise and quietness is ensured because the electric motor is used as a drive source. However, since the electric motor is disposed near the cutting blade at the distal end of the operating arm, the center of gravity is close to the distal end of the operating arm when the operator carries the bush cutter by placing the strap around the shoulder. Therefore, it is difficult to move the distal end of the operating arm in the front-rear and left-right directions. As a result, work efficiency is reduced and the burden on the operator is increased.
The cooling air used for cooling the electric motor is discharged into the atmosphere through the outlet formed in the motor housing. Therefore, foreign matters such as dust generated when weeds and the like are cut by the rotating cutting blade tend to enter the motor housing through the outlet. These foreign matters cause abrasion of rotating components, such as bearings, and reduce endurance of the electric motor. In addition, the outlet is easily clogged with weeds and the like that are cut by the cutting blade. If this happens, the flow of the cooling air is degraded and performance in cooling the electric motor and the like is reduced.
Furthermore, the battery and the electric motor must be connected to each other with long wires, which requires cumbersome tasks of wiring and maintenance. In addition, a battery with a large capacity is required, and use of such a battery leads to an increase in the weight of the bush cutter.
These problems occur not only in bush cutters, but also in other kinds of portable power working machines having an electric motor and an actuating part at a distal end of an operating arm.